A memorial is to be created for victims and survivors of the four terror attacks in London last year.
The tribute has been set up to mark the four terrorist atrocities that took place in the city last year, at Westminster Bridge, London Bridge, Finsbury Park and Parsons Green.
Tomorrow (March 22) will be exactly one year since Khalid Masood ploughed into pedestrians on Westminster Bridge before fatally stabbing unarmed police officer Keith Palmer.
Messages will be able to be left in a digital book of hope at City Hall from tomorrow (March 22) onwards, for the installation which will be in place until June.
Social media will also allow people to send messages by using the hashtag #LondonUnited and the messages will be projected onto a London map.
The phrase #LondonUnited will also be projected on to the Houses of Parliament, London Bridge, Finsbury Park Mosque and Parsons Green Tube station on the anniversaries of the four attacks.
Mayor Sadiq Khan said: "Londoners will never forget the horrific terror attacks on our city in 2017. We will never forget the bravery of our emergency services and first responders who ran towards danger while urging the rest of us to run to safety.
"And we will never forget the courage of PC Keith Palmer, who paid the ultimate sacrifice whilst protecting Parliament.
"These were not only attacks on our city and our country, but on the very heart of our democracy and the values we cherish most, freedom, justice and tolerance.
"I hope these arrangements will help people to come together and remember those who were killed and injured, to show solidarity and support for their families and friends and the people whose lives have been affected by these tragic attacks."
Five innocent people were killed in Masood's rampage, PC Palmer, who was on duty at the Palace of Westminster, along with US tourist Kurt Cochran, Romanian tourist Andreea Cristea and Britons Aysha Frade and Leslie Rhodes, who were mown down on the bridge.
The planned memorial was agreed following meetings with bereaved families, survivors, members of the emergency services and local councils.